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Re: Sloping terrain Re: Woman against Abelisaur
On 7/25/2011 3:34 AM, David Marjanovic wrote:
It would be that way if all else had been equal. But it wasn't.
theropods had long, somewhat spreading toes; such feet don't sink in
True again, but we are considering the case where sinking occurs, are we
but are easy to pull out because the toes taper and can be
I have doubts about this model -- after all, the tridactyl foot
logically has a much greater surface area per unit available power than
the columnar one, and I question the idea that the 'drag profile' upon
w/drawal is actually lower in absolute terms.
Further, consider a substrate wherein the overlying seds yield very
easily to a depth of 1m, and then adequate footing is found -- in the
event that the toe-tip catches on a root or rock while in transit to the
bottom, you now have a short lever under great downward pressure -- if
the root or rock does not give way, the toe might. If the underlying
'bottom' is also uncertain, as most are, problems can easily begin to
In any case, the biped now is both at risk of injury, and/or on uneven
footing, therefore unstable.
Again, the human body gives a chance to experience the reality -- push
your open hand into soft mud and w/draw it -- then try it with closed fist.
The quadruped w/ columnar feet has no such problems. Splayed toes do
help to prevent sinking, but once sinking occurs, they are a liability.
All sauropods had compact feet and outright columnar
hands that must have sunk in easily and must have created suction when
At the risk of creating 'collateral humor', I have to state that suction
is highly over-rated.
In most seds, wiggling a limb embedded in mud creates low density zones
immediately surrounding the limb -- and (again, in most seds) these
zones are temporarily filled w/ watery fluids that are less solid than
the surrounding substrate.
In the unusual cases wherein solid components immediately rush in to
fill the void, I assert based on personal observation that columns are
easier to w/draw than splayed toes, even if the toes do 'fold up'. This
concept, at least, can be thoroughly tested w/ mechanical models.
Lastly, a quad w/ columnar feet can apply much more withdrawal force per
limb than a biped w/ tridactyl feet. More stable platform to pull from,
more power per limb, and lower surface to power ratio...
The intuitive 21st century perceptions just do not work when examined